Concrete is an important and well-known structural material. It is used primarily as a paving material, but also to provide foundations, and other structural components. Concrete is a mixture of cement and aggregates. The most common cement is Portland cement, but other binding materials are also well-known and commonly used. The aggregates include rocks, sand, and other similar materials of varying sizes. The dry cement is mixed with water and the aggregate to form the concrete. Additionally, various other chemicals and admixtures may be included in the mixture depending upon the intended use of the concrete, as well as environmental factors such as temperature and relative humidity at the time the concrete is being mixed and poured.
Traditionally, concrete has been mixed in relatively large stationary mixing plants, and then loaded on to a truck with a rotating barrel to be transported to a job site. The rotating barrel keeps the concrete mixer flowable and mixed, until the truck can arrive at the job site.
Recently, mobile concrete mixing units have been developed that mix and dispense the concrete at the job site as it is needed. This is advantageous as it eliminates the need for transporting the wet concrete mixture. Additionally, it takes a lot of the guesswork out of trying to get the proper mixture to match the conditions at the job site. Moreover, many concrete mixtures begin deteriorating after they are mixed, and are subject to spoilage before they reach the job site. Some of these mobile concrete mixtures are of a volumetric nature, as opposed to a batch nature. That means that the stream of concrete leaving the mixer should be uniform at each time the mixture is being dispensed. In other words, the ratio of components in any given volume of the mixture should be uniform. In a batch system it is only necessary to assure that the ratio of ingredients in the entire batch matches a set standard.
The present invention is directed to overcoming challenges associated with volumetric mobile concrete mixers. Such mobile volumetric mixers commonly use hydraulics to mix the various components of the concrete. Because a concrete is relatively bulky and heavy the hydraulic systems can generate a lot of heat in the hydraulic fluid that needs to be dissipated. This can require a large volume of hydraulic fluid.
In cooler climates, as the air temperature approaches and drops below the freezing point of water, it can be difficult or impossible to mix and pour concrete that is structurally sound. In some climates this can significantly limit the number of days the mobile mixing unit can be used. Using warmer water can help in some cases, and will permit the mixing and pouring of concrete in colder temperatures; however, the water can quickly cool if its container is not insulated or heated.
Commonly, the volumetric mobile mixers include an aggregate bin situated above a moving belt. The belt is used to deliver the aggregate to a mixing area where it is mixed with the dry cement powder and water. It is known to divide the aggregate bin into separate chambers above the belt such that two types of aggregate may be included in the bin and mixed into the concrete. In these divided chambers, occasionally the weight of the aggregate upon itself can cause it to pack tightly enough to form a bridge between the divider and the sidewall of the bin once the belt starts moving, such that the aggregate stops freely flowing onto the belt. This can cause non-uniform mixtures. The bridging issue can be especially acute in cold temperatures when moisture within the aggregate can cause the aggregate to freeze together.
Another difficulty with mobile volumetric mixers is that the large volume of water can cause the unit to be unstable, especially when the water sloshes from side-to-side of the water storage tank during transportation, and also if the unit is on a significant side grade.
Another difficulty with using mobile volumetric mixers during cold weather is maintaining the water at a sufficiently high temperature to properly activate the cement.
A further issue related to mobile concrete mixers is the stability of the vehicle when cornering or driving on a side grade. The water tank can make the vehicle top heavy, and can cause the center of gravity to shift laterally as back and forth as the water sloshes within the tank.
Therefore, an objective of the present invention is to provide an improved volumetric concrete mixing system that includes a water tank within the aggregate bin.
It is another object of the present invention to provide a hydraulic fluid reservoir within the water tank in order to remove heat from the hydraulic fluid and warm the water.
It is a further objective of the present invention to provide a water tank within an aggregate bin of a volumetric mobile concrete mixer, such that the water tank serves to divide the aggregate bin into two separate compartments while also reducing the likelihood of bridging occurring within the aggregate.
It is a further object of the present invention to provide a mobile volumetric concrete mixer that has improved performance in cold temperatures.